1. Field of the Invention
The present invention relates to signature generation processing and signature verification processing.
2. Description of the Related Art
Recent rapid advancement and spread of computers and networks have resulted in digitization of various data, such as character data, image data, and audio data.
Digital data can be stored in perfect condition indefinitely without deterioration, such as aging. However, copying, editing, and processing can easily be performed thereon.
The copying, editing, and processing of the digital data are very useful to users, while protection of the digital data is a serious problem. Therefore, security technology rapidly increases in importance.
Accordingly, a technology called a digital signature has been proposed as a method of verifying additional falsification-proof data to enable a recipient to determine whether data transmitted to him is falsified. A digital signature technology has advantages in preventing not only data falsification but also Internet impersonation and repudiation.
Japanese Patent Application Laid-Open No. 2003-132028 has proposed a system configured to transmit digital data by preliminarily applying a digital signature technology thereto and to perform, when receiving the digital data to which a digital signature is added, verification processing on the digital signal applied thereto.
Although there are less serious problems in a case where a size of signed data to be received is small, the system described in Japanese Patent Application Laid-Open No. 2003-132028 cannot verify signed data in real time in synchronization with reception thereof especially in a case where the size of the signed data to be received is large. Also, it is necessary for verifying signed data to receive the entirety of the signed data. Thus, even when digital data or signed data is falsified, the entirety of the data should be received.
A system disclosed in U.S. Pat. No. 5,898,779 is configured to produce a digital signature that is not associated with the entire image but with a partial area of the image. This system can verify whether partial area data is falsified.
Although the system disclosed in U.S. Pat. No. 5,898,779 can verify whether partial area data is falsified, this system cannot verify association between image data and partial area data. Therefore, for example, even in a case where the partial area data is not included in the image data, or where the partial area data is a missing part of the image data, this system cannot verify validity of the image data.